Estimating non-specific aquatic toxicity for the fathead minnow using surrogate chromatographic models

We compileda data base of 250 dischargers across the United States and examined relationships between standardized Ceriodaphnia dubia and Pimephales promelas (fathead minnows), whole effluent toxicity (WET) test endpoints, and instream biological condition as measured by benthic macroinvertebrate assessments. Sites were included in the analysis if the effluents were not manipulated before testing (e.g., dechlorination), and standardized biological and physical habitat assessment methods were used upstream and directly downstream of the discharge. Several analyses indicated that fish endpoints were more related to instream biological condition than Ceriodaphnia WET endpoints. Dischargers that failed <25% of their tests had ≤15% chance of exhibiting instream impairment. Effluent dilution was the strongest factor affecting relationships between WET and observed biological conditions. Effluents that comprised >80% of the stream under low-flow conditions exhibited better relationships between WET and instream condition than effluents with greater dilution. Effluents that comprised <20% of the stream had a low probability of exhibiting impairment, even if several WET test failures were observed over a 1-year period. Fish acute and chronic WET information could predict instream biological conditions; however, WET compliance, based on 7Q10 stream flow, was consistently conservative. Our results indicate that WET was more predictive of instream biological condition if several tests were conducted, more than one type of test was conducted, and endpoints within a test were relatively consistent over time.

Acute toxicity of 12 industrial chemicals to freshwater and saltwater organisms

The potential toxicity to human and aquatic receptors of petroleum fuel biodegradation metabolites (oxygen‐containing organic compounds [OCOCs]) in groundwater has been investigated as part of a multi‐year research program. Whole mixtures collected from locations upgradient and downgradient of multiple fuel release sites were tested using: 1) in vitro screening assays for human genotoxicity (the gamma‐H2AX assay) and estrogenic effects (estrogen receptor transcriptional activation assay), and 2) chronic aquatic toxicity tests in 3 species (Ceriodaphnia dubia, Raphidocelis subcapitata, and Pimephales promelas). In vitro screening assay results demonstrated that the mixtures did not cause genotoxic or estrogenic effects. No OCOC‐related aquatic toxicity was observed and when aquatic toxicity did occur, upgradient samples typically had the same response as samples downgradient of the release, indicating that background water quality was impacting the results. This information provides additional support for previous work that focused on the individual compounds and, taken together, indicates that OCOCs from petroleum degradation at fuel release sites are unlikely to cause toxicity to human or freshwater receptors at the concentrations present. Environ Toxicol Chem 2020;39:1634–1645. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

The performance of chromatographic systems to mimic aquatic toxicity to the fathead minnow fish is evaluated taking into account the factors that contribute to the variance of biological-chromatographic correlations. These factors are the precision to measure the fathead minnow toxicity, the precision of the surrogate chromatographic system, and the error from the dissimilarity between the fathead minnow and chromatographic systems. The precisions are estimated through the characterization of the systems by the solvation parameter model. Several chromatographic systems as well as the common reference octanol-water partition system have been selected to test their ability to model the nonspecific toxicity to the fathead minnow by means of the proposed approach. Predictions and experimental tests show that the micellar electrokinetic chromatography system of sodium taurocholate and chromatographic measurements using an immobilized artificial membrane column provide the most precise estimations of this biopartitioning property. The octanol-water partition system, the conventional C18 high-performance liquid chromatography systems, and the micellar electrokinetic chromatography system of sodium dodecylsulfate show worse performances.

DIGE and iTRAQ as biomarker discovery tools in aquatic toxicology

The widespread use of chemical products inevitably brings many side effects as environmental pollutants. Toxicological assessment of compounds to aquatic life plays an important role in protecting the environment from their hazards. However, in vivo animal testing approaches for aquatic toxicity evaluation are time-consuming, expensive, and ethically limited, especially when there are a great number of compounds. In silico modeling methods can effectively improve the toxicity evaluation efficiency and save costs. Here, we present a web-based server, AquaticTox, which incorporates a series of ensemble models to predict acute toxicity of organic compounds in aquatic organisms, covering Oncorhynchus mykiss, Pimephales promelas, Daphnia magna, Pseudokirchneriella subcapitata, and Tetrahymena pyriformis. The predictive models are built through ensemble learning algorithms based on six base learners. These ensemble models outperform all corresponding single models, achieving area under the curve (AUC) scores of 0.75-0.92. Compared to the best single models, the average precisions of the ensemble models have been increased by 12-22%. Additionally, a self-built knowledge base of the structure-aquatic toxic mode of action (MOA) relationship was integrated into AquaticTox for toxicity mechanism analysis. Hopefully, the user-friendly tool (https://chemyang.ccnu.edu.cn/ccb/server/AquaticTox); could facilitate the identification of aquatic toxic chemicals and the design of green molecules.

Predicting biophysical properties of small molecules from chromatographic measurements and the solvation parameter model

There are more than 70000 chemicals in use today and many more being synthesized. It is vital to assess the influence of these compounds on the environment and on human health. Experimental testing is both time-consuming and expensive, and accordingly, there is a pressing requirement for accurate in silico methods to assess the toxicity. QSAR studies of the environmental fate of chemicals are widely used for this purpose. One of the broadly used toxicity database is the Distributed Structure-Searchable Toxicity (DSSTox) database from the U.S. Environmental Protection Agency (http://www.epa.gov). It provides various data including EPA Fathead Minnow Aquatic Toxicity Database (EPAFHM), which currently contains structures of 617 chemicals of which 580 structures have toxicity data (EPAFHM_v3b_617_10Apr2006). The toxicity end-points are based on the 96 h LC50 (mmol/L) values for the fathead minnow, which used for standard toxicity test described by the U.S. Environmental Protection Agency. We used QNA (Quantitative Neighbourhoods of Atoms) descriptors and Self-Consistent Regression for QSAR modeling of acute toxicity in the fathead minnow. The statistical parameters of the correlation are the follows: N = 580, R2 = 0.804, F = 32.508, SD = 0.670, Q2 = 0.759. For 522 compounds (90%), the deviation of the predicted values from the observed ones is less than 1 logLC50 (mmol/L). Leave-10%-out cross-validation procedure was used for assessment of prediction ability of the method. It was performed 20 times and average R2 of prediction was 0.606, the highest value of R2 = 0.815, the lowest value of R2 = 0.501. Applicability domain was estimated for test set by leave-10%-out cross-validation procedure. These results confirmed robustness and satisfactory predictive ability of the method, hence, it can be used for computational assessment of acute toxicity in new compounds.

Watersheds have historically been used as the appropriate spatial classification unit for managing water resources. However, geology, soil type, predominant vegetation, and climate have obvious influences on water quality and are not constrained by watercourses or political boundaries. This concept has evolved for several decades and developed the concept of ecoregions and other spatial schemes. While this approach to water resource management has considered the interaction between water quality and biological integrity (aquatic community structure and assemblage), it has not been applied in the context of predicting aquatic toxicity. As such, a previously published study providing a chemical and toxicological data set consisting of 24 sampling sites in South Carolina, USA, and was used to develop empirical models for predicting acute copper (Cu) toxicity to larval fathead minnows (Pimephales promelas). Moreover, numerous spatial classifications (hydrologic units, ecoregions, stream order, adjacent land use, and proximity to certain land uses) and seasonality were used to delineate sites and develop empirical models based on these different classifications. An independent sampling and testing regime was implemented to determine the performance of the empirical models and whether certain classifications could be used to extrapolate toxicity data across spatial landscapes. Additionally, a computational model (biotic ligand model [BLM]) for deriving site-specific water quality criteria for Cu also was used as a reference for current regulatory application. Empirical models based on delineations of stream order, hydrologic unit, and downstream distance to urbanization accurately predicted at least 60% of the observed Cu toxicity values within the supplemental data set. Delineations based on adjacent land use, ecoregions, and seasons were not as useful for predicting acute Cu toxicity but demonstrated better performance than the BLM.

Discrimination of the acute toxicity of chemicals to guppy (Poecilia reticulata), fathead minnow (Pimephales promelas) and rainbow trout (Oncorhynchus mykiss) with nonpolar narcosis and other Modes Of Action (MOA) was successfully carried out by means of discrimination analysis and structural similarity analysis. Good QSARs for acute aquatic toxicity of chemicals with nonpolar narcosis MOA for the three fish species were constructed, based on molecular polarizability and H‐bond acceptor factors calculated by the HYBOT program. These latter relationships are useful alternatives to QSARs based on the experimental parameter log Ko/w because they yield good statistics and because they are amenable to physicochemical interpretation. In this case, the acute aquatic toxicity of chemicals with nonpolar MOA is presented as the result of two contributions (molecular polarizability, which is volume‐related, and hydrogen bonding) with opposite action: molecular polarizability increases acute nonpolar narcosis toxicity and H‐bond acceptor ability decreases it.

Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) are two major groups of PFAS will be subjected to the Maximal Contamination Concentration (MCL) of 4 ng/l in drinking water to be implemented by the U.S. EPA by 2025. How to accurately predict toxicity of PFAS with varied carbon chain length is important for treatment and sequential removal from drinking water. This study presents Quantitative Structure and Activity Relationship (QSAR) models developed through both linear regression and two order regression. Log P is compiled from reference and carbon content is counted as the molecule represented. Bioconcentration potential is predicted from CompTox.The results suggest that as log P and carbon content increase, the bioconcentration potential of PFCAs also increases. In other words, larger PFCA molecules tend to be easier to bioaccumulate in living organisms. This finding is crucial because bioconcentration refers to the accumulation of substances from water directly into living organisms through the process of passive diffusion across cell membranes. On the other hand, 96-hour fathead minnow LC50 has an inverse relationship, with higher LC50 values associated with lower log P and fewer carbons. The varying R-squared values across methods indicate differing degrees of correlation, underscoring the impact of compound structure on aquatic toxicity. Similarly, for oral rat LD50 and 48-hour D. magna LC50, the R-squared values reflect moderate to strong correlations with log P and the number of carbons. As the log P and carbon content decrease,the toxicity expressed in LC50 or LD50 increases. This relationship underscores the role of chemical properties in influencing the toxicity of PFCAs across different organisms and exposure routes. For instance, the negative correlation between log P and aquatic toxicity (96-hour fathead minnow LC50 and 48-hour D. magna LC50) suggests that compounds with higher hydrophobicity (higher log P) and more carbons may exhibit lower acute toxicity to aquatic organisms.

The acute toxicity of N-nitrosodimethylamine (DMN) and N-nitrosodiethylamine (DEN) was determined for three groups of aquatic organisms: algae, invertebrates, and fish. Toxicity of DMN and DEN to algae was assessed as a repression in the growth rate of either Selenastrum capricornutum or Anabaena flos-aquae in static bioassay tests. DMN and DEN concentrations of 1-10 ppm depressed algal growth in all cases. Invertebrate toxicity was determined in 96-h static bioassay tests with Dugesia dorotocephala and Gammarus limnaeus. The data indicated that these organisms are not highly susceptible to nitrosamine toxicity. The 96-h LC50s for D. dorotocephala were 1365 and 1490 ppm for DMN and DEN, respectively. Similar studies with G. limnaeus indicated LC50s of 330 and 500 ppm for DMN and DEN, respectively. Fish toxicity was also determined in 96-h statis bioassays with the fathead minnow (Pimephales promelas). Acute toxicities were calculated as LC50s of 940 and 775 ppm for DMN and DEN, respectively. Algae were calculated as LC50s of 940 and 775 ppm for DMN and DEN, respectively. Algae were quite sensitive to relative low levels of volatile nitrosamines, but higher organisms (invertebrates and fish) were relatively insensitive.

Toxicity of substances in seawater was measured using growth inhibition of embryonic sea urchins during a short period after fertilization. Growth of Arbacia punctulata embryos was monitored by incorporation of tritium-labeled thymidine, a nucleoside incorporated into newly synthesized deoxyribonucleic acid (DNA). Sensitivity and ranking ability of this rapid Arbacia embryo test were judged by comparison of toxicity values for several organic industrial chemicals using this test and two standard acute aquatic toxicity tests. Median effective toxicity values (EC50 values) for early embryos compared favorably to median lethal values (LC50 values) obtained in standard acute toxicity tests using Pimephales promelas (fathead minnow) and Daphnia magna (water flea). This paper presents a comparison of toxicant exposure procedures using the Arbacia embryo thymidine incorporation test. Toxicant exposure began before, at the time of, or after fertilization and continued for 4 h following fertilization. In addition to the eight organic chemicals tested for comparison to acute toxicity values for other species, several chemicals with embryotoxic potentials (tumor promoters and teratogens) were tested to determine differential sensitivities of exposed life-stages: unfertilized egg, fertilization, and early embryo. EC50 values for any one substance were not significantly changed by exposure modification. Toxicity values for exposures that included fertilization as well as early embryo growth were at least as sensitive as post-fertilization exposure values for all compounds tested except one. Because of technical ease and potential sensitivity, toxicant exposure that includes fertilization as well as early embryo growth (but not unfertilized egg exposure) is recommended for future testing. Additional development, refinement, and standardization of this fertilization and early embryo test should further increase its utility in toxicity testing. Because this test requires only 4 h to exposure and can be correlated with standard measurements of toxicity, it could be used in early stage hazard evaluation in conjunction with other aquatic bioassays.

Rapid Toxicity Assessment Using an in Vivo Enzyme Test for Brachionus plicatilis (Rotifera)

Fungicides play an important role in crop protection, but they have also been shown to adversely affect non-target organisms, including those living in the aquatic environment. The aim of the present study is to combine experimental and computational approaches to evaluate the effects of flutriafol, metconazole, myclobutanil, tebuconazole, tetraconazole and triticonazole on aquatic model organisms and to obtain information on the effects of these fungicides on Lemna minor, a freshwater plant, at the molecular level. The EC50 (the half-maximum effective concentration) values for the growth inhibition of Lemna minor in the presence of the investigated fungicides show that metconazole (EC50 = 0.132 mg/L) and tetraconazole (EC50 = 0.539 mg/L) are highly toxic, tebuconazole (EC50 = 1.552 mg/L), flutriafol (EC50 = 3.428 mg/L) and myclobutanil (EC50 = 9.134 mg/L) are moderately toxic, and triticonazole (EC50 = 11.631 mg/L) is slightly toxic to this plant. The results obtained with the computational tools TEST, ADMETLab2.0 and admetSAR2.0 also show that metconazole and tetraconazole are toxic to other aquatic organisms: Pimephales promelas, Daphnia magna and Tetrahymena pyriformis. A molecular docking study shows that triazole fungicides can affect photosynthesis in Lemna minor because they strongly bind to C43 (binding energies between −7.44 kcal/mol and −7.99 kcal/mol) and C47 proteins (binding energies between −7.44 kcal/mol and −8.28 kcal/mol) in the reaction center of photosystem II, inhibiting the binding of chlorophyll a to these enzymes. In addition, they can also inhibit glutathione S-transferase, an enzyme involved in the cellular detoxification of Lemna minor.